JP5706283B2 - Destination station and channel estimation method - Google Patents

Description

  The present invention relates to a cooperative transmission technique in which a transmission station and a relay station transmit radio signals to a destination station.

  In recent years, cooperative transmission (cooperative communication scheme) that improves communication characteristics by causing cooperative radio transmission (cooperative transmission) to be performed by radio stations (relay stations) other than the source station and the destination station has attracted attention. The system model of cooperative transmission is mainly determined by the three elements of the relay station forward method, the cooperative system configuration, and the cooperative protocol.

  The relay station forward method indicates what kind of signal processing is performed on a signal received by the relay station and forwarded to the destination station. Specific examples of the relay station forward method include a DF (Decode-and-Forward) method and an AF (Amplify-and-Forward) method. In the DF method, the relay station decodes and reproduces the received signal and then transfers it to the destination station. In the AF method, the relay station does not decode and reproduce the received signal, but simply performs amplification before transferring it to the destination station.

  The cooperative system configuration indicates the number of radio stations (originating station, relay station, destination station) configuring a cooperative transmission system (cooperative transmission system) and the number of cooperative relay hops performed in the cooperative transmission system. The simplest cooperative system configuration is a configuration in which one relay station (Relay; R) exists between a source station (Source; S) and a destination station (Destination; D). Such a configuration is called 1-Relay 2-Hop (1R2H). In the 1R2H configuration, one slot of radio resources (time or frequency) is generally allocated to communication from the transmission station to the relay station and communication from the relay station to the destination station. Therefore, it is often considered that one period of the entire cooperative system is 2 slots.

The cooperative protocol indicates a combination of transmission / reception relationships between wireless stations within one cycle of the entire cooperative transmission system.
With regard to such cooperative transmission, as described in Non-Patent Document 1 and Non-Patent Document 2, for example, many studies have been conducted as techniques for improving communication characteristics.

RU Nabar, H. Bolcskei, and FW Kneubuhler, “Fading relay channels: Performance limits and space-time signal design,” IEEE J. Sel. Areas Commun., Vol. 22, no. 6, pp. 1099-1109, Jun . 2004. "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-speed Physical Layer in the 5GHz band," IEEE Std. 802.11a-1999

  In the coordinated transmission system, the transmitting station and the relay station transmit different signals in the same time slot. In this case, the destination station receives a composite wave of the signal transmitted from the transmission station and the signal transmitted from the relay station. For this reason, the training signals attached to the signals interfere with each other, and the estimation accuracy of the channel information decreases. As a result, there has been a problem that the decoding accuracy between the signal transmitted from the transmission station and the signal transmitted from the relay station is lowered.

  In view of the above circumstances, an object of the present invention is to provide a technique for improving channel information estimation accuracy in a destination station in a cooperative transmission system that transmits different signals at the same timing between a transmission station and a relay station.

  One aspect of the present invention includes a first signal transmitted from a transmission station at a first timing, a second signal transmitted from the transmission station at a second timing that arrives after the first timing, Based on a signal reception unit that receives the first signal relayed by the relay station at a second timing, and a known signal included in the first signal transmitted from the transmission station at the first timing , A first channel estimation unit that estimates first channel information that is channel information related to the first signal transmitted from the source station at the first timing, an estimation result of the first channel information, and the first A first transmission power which is a transmission power when the transmission station transmits the first signal at a timing of a first transmission power which is a transmission power when the transmission station transmits the second signal at the second timing. 2 sending A second channel estimation unit that estimates second channel information that is channel information related to the second signal transmitted from the transmission station at the second timing based on power, the first channel information, and the first channel information. Based on the estimation result of 2-channel information and the first transmission power and the second transmission power, the transmission is transmitted from the transmission station at the first timing and relayed by the relay station at the second timing. And a third channel estimation unit that estimates third channel information that is channel information related to the first signal.

  One aspect of the present invention includes a first signal transmitted from a transmission station at a first timing, a second signal transmitted from the transmission station at a second timing that arrives after the first timing, Based on a signal reception step of receiving the first signal relayed by the relay station at a second timing, and a known signal included in the first signal transmitted from the source station at the first timing , A first channel estimation step for estimating first channel information that is channel information related to the first signal transmitted from the transmitting station at the first timing, an estimation result of the first channel information, and the first The first transmission power, which is the transmission power when the transmission station transmits the first signal at the timing of, and the transmission power when the transmission station transmits the second signal at the second timing, A second channel estimation step of estimating second channel information that is channel information related to the second signal transmitted from the transmitting station at the second timing based on a certain second transmission power; and the first channel Information and the estimation result of the second channel information, and the first transmission power and the second transmission power, and transmitted from the transmission station at the first timing and the relay station at the second timing. A third channel estimation step of estimating third channel information that is channel information related to the first signal relayed by the first signal.

  According to the present invention, it is possible to improve channel information estimation accuracy in a cooperative transmission system in which different signals are transmitted at the same timing between a transmission station and a relay station. Therefore, each signal can be accurately separated at the destination station that has received different signals transmitted at the same timing in the cooperative transmission system. This also makes it possible to obtain diversity gain by cooperative transmission.

It is a system configuration figure showing the system configuration of the cooperative transmission system in one embodiment of the present invention. It is a schematic block diagram showing the function structure of each apparatus of the cooperative transmission system in one Embodiment of this invention. It is a figure which shows the outline of communication in a cooperative transmission system. It is a figure which shows the specific example of the signal transmitted in each slot. It is a figure which shows the specific example of the transmission timing of the signal transmitted in each slot. It is a flowchart which shows the flow of a process of the destination station of the cooperative transmission system in one Embodiment of this invention.

  FIG. 1 is a system configuration diagram showing a system configuration of a cooperative transmission system 1 according to an embodiment of the present invention. The cooperative transmission system 1 includes a transmission station 1-1, a relay station 1-2, and a destination station 1-3. The cooperative transmission system 1 has a cooperative system configuration of 1R2H (1-Relay 2-Hop). In the coordinated transmission system 1, radio resources (time) are respectively used for communication from the transmission station 1-1 to the relay station 1-2 and the destination station 1-3, and communication from the relay station 1-2 to the destination station 1-3. (Or frequency) slot is allocated.

  FIG. 2 is a schematic block diagram showing a functional configuration of each device of the cooperative transmission system 1 according to the embodiment of the present invention. First, the configuration of each device of the cooperative transmission system 1 will be described. Each of the transmission station 1-1, the relay station 1-2, and the destination station 1-3 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like connected by a bus, and executes predetermined programs. Function. All or some of the functions provided in each device may be realized by using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The program of each device may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. The program of each device may be transmitted via a telecommunication line.

  The transmission station 1-1 includes a channel encoding unit 11, a data modulation unit 12, a distribution unit 13, a training addition unit 14, a passband conversion unit 15, and an antenna 16. The destination station 1-3 includes an antenna 31, a baseband conversion unit 32, a channel estimation unit 33, a data demodulation unit 34, and a channel decoding unit 35.

  FIG. 3 is a diagram illustrating an outline of communication in the cooperative transmission system 1. The slot represents the timing at which the wireless station (generic name for the transmitting station 1-1, the relay station 1-2, and the destination station 1-3) performs communication. Slot 1 is a slot immediately before slot 2. Time T1 and time T2 correspond to the time at which slot 1 and slot 2 start, respectively. In slot 1, the transmitting station 1-1 broadcasts the signal P1 to the relay station 1-2 and the destination station 1-3. In slot 2, which comes after slot 1, the transmitting station 1-1 and the relay station 1-2 transmit signals to the destination station 1-3. At this time, the transmitting station 1-1 transmits the signal P2, and the relay station 1-2 transmits the signal P1. The signal P1 and the signal P2 are different signals. Therefore, the destination station 1-3 receives a combined wave of the signal P2 transmitted from the transmission station 1-1 and the signal P1 transmitted from the relay station 1-2 in the slot 2. Hereinafter, the composite wave received by the destination station 1-3 in the slot 2 is referred to as a received signal.

  The destination station 1-3 receives two types of signals (signal P1 and signal P2) in slot 1 and slot 2. Such a cooperation protocol is called a protocol I or a MIMO (Multiple Input Multiple Output) type.

  Hereinafter, a communication flow in the cooperative transmission system 1 will be described with reference to FIGS. 2 and 3. First, the channel encoding unit 11 of the transmission station 1-1 performs channel encoding processing on the information bit stream to be transmitted, and generates encoded bits. Subsequently, the data modulation unit 12 of the transmission station 1-1 constellation-maps the coded bits according to an arbitrary rule (for example, gray coding) to generate a complex QAM symbol. The distribution unit 13 of the transmission station 1-1 distributes the complex QAM symbols into two different streams (complex QAM symbol streams).

  The training adding unit 14 of the transmission station 1-1 generates a transmission signal (corresponding to a subpacket described later) by adding training signals and the like to the two complex QAM symbol streams. At this time, the training addition unit 14 adds the same training signal to two different streams distributed. The passband conversion unit 15 converts each signal from baseband to passband, and transmits the signal from the antenna 16 in different slots. For example, when the complex QAM symbol stream 1 and the complex QAM symbol stream 2 are generated, the passband converting unit 15 of the transmitting station 1-1 transmits a signal including the complex QAM symbol stream 1 in the slot 1, and the slot 2 transmits a signal including the complex QAM symbol stream 2.

  The baseband conversion unit 32 of the destination station 1-3 receives a signal via the antenna 31. The baseband conversion unit 32 converts the received signal from the passband to the baseband. The channel estimation unit 33 performs channel estimation based on the training portion of the received signal. The data demodulator 34 equalizes the channel of the signal based on the result of channel estimation by the channel estimator 33, and performs data demodulation processing. The channel equalization here refers to a signal (received signal) obtained by combining a signal transmitted from the transmitting station 1-1 in slot 2 and a signal transmitted from the relay station 1-2 in slot 2. Includes processing to separate the signals.

  The data demodulator 34 generates a detection value corresponding to each complex QAM symbol by performing data demodulation processing. The channel decoding unit 35 performs channel decoding processing based on the detection value. By executing the channel decoding process, the channel decoding unit 35 restores the information bit stream that is the transmission target in the transmission station 1-1.

  FIG. 4 is a diagram illustrating a specific example of a signal transmitted in each slot. FIG. 5 is a diagram illustrating a specific example of transmission timing of a signal transmitted in each slot. Hereinafter, the details of the communication processing in the cooperative transmission system 1 will be described with reference to FIGS. In the following description, a signal transmitted in each slot is referred to as a “subpacket”, and a set of subpackets including a plurality of complex QAM symbol streams generated from one information bitstream is referred to as a “packet”. For example, a signal including the complex QAM symbol stream 1 and a signal including the complex QAM symbol stream 2 are each a subpacket, and a set of these two subpackets is a packet.

  Each signal has a portion including a training signal (training signal portion) and a portion including a QAM symbol stream generated from an information bit stream to be transmitted (data portion). In FIG. 4, the rectangles described as “P1 training” and “P2 training” correspond to the training signal portion. The rectangles described as “P1 data” and “P2 data” correspond to data portions. The data portion is composed of a plurality of data blocks, and a QAM symbol stream is stored in each data block.

The complex QAM symbol value stored in the data portion of the signal P1 transmitted from the transmitting station 1-1 in the slot 1 is assumed to be X1. Let X2 be the complex QAM symbol value stored in the data portion of the signal P2 transmitted from the transmitting station 1-1 in slot 2.
Also, let C be the complex QAM symbol value of the training signal. Each signal is converted from baseband to passband and transmitted in the corresponding slot. The transmitting station 1-1 transmits the signal P2 after the time D_s has elapsed after transmitting the signal P1. On the other hand, the relay station 1-2 transmits the signal P1 after the elapse of time D_r after the transmission of the signal P1 by the transmission station 1-1.

In slot 1, the transmission station 1-1 performs broadcast transmission to the relay station 1-2 and the destination station 1-3. The received signal at the destination station 1-3 in the slot 1 is expressed by the following formula 1.
In the following description, A_B represents that B is attached as a subscript to A. [A] represents the square root of A. {A} indicates that a hat (^) is attached to the upper part of A, and indicates an estimated value of A.

  P_s1 represents the transmission power of the transmitting station 1-1 in slot 1. H_sd represents a channel response between the source station 1-1 and the destination station 1-3. W_d1 represents additive white Gaussian noise (AWGN) in the destination station 1-3 of the slot 1. The value of P_s1 is known in the channel estimation unit 33 of the destination station 1-3.

The reception signal Y_r1 at the relay station 1-2 in the slot 1 is expressed by the following equation 2.

  H_sr represents a channel response between the transmission station 1-1 and the relay station 1-2. W_r1 represents AWGN (white additive Gaussian noise) at the relay station 1-2 in the slot 1. The signal Y_r1 received by the relay station 1-2 in the slot 1 is amplified by the amplification coefficient α_γ and transmitted to the destination station 1-3 in the slot 2.

In slot 2, the transmitting station 1-1 and the relay station 1-2 transmit signals to the destination station 1-3. Since both are transmitted simultaneously, the received signal Y_d2 at the destination station 1-3 in the slot 2 is expressed by the following Equation 3.

  Here, P_r2 represents the transmission power of relay station 1-2 in slot 2. Therefore, [(P_s1) (P_r2)] represents the product of the transmission power of the transmission station 1-1 in slot 1 and the transmission power of the relay station 1-2 in slot 2. P_s2 represents the transmission power of the transmitting station 1-1 in slot 2. The values of P_s2 and P_r2 are known in the channel estimation unit 33 of the destination station 1-3, similarly to the value of P_s1.

From Equation 1 and Equation 3, the following Equation 4 is established.

  In Expression 4, H_11 represents channel information (hereinafter referred to as “first channel information”) of a propagation path between the transmitting station 1-1 and the destination station 1-3 in the slot 1, and H_21 is transmitting in the slot 1. The channel information of the propagation path transmitted from the station 1-1 and reaching the destination station 1-3 via the relay station 1-2 in the slot 2 (hereinafter referred to as “third channel information”), H_22 represents the slot 2 The channel information (hereinafter referred to as “second channel information”) of the propagation path between the source station 1-1 and the destination station 1-3 in FIG. Each value is expressed as follows.

  The channel estimation unit 33 of the destination station 1-3 estimates each value of H_11 (first channel information), H_21 (third channel information), and H_22 (second channel information). The estimation process of each value is as follows.

  First, the channel estimation unit 33 estimates the first channel information based on Equation 1 using the training signal received in the slot 1. Specifically, the channel estimation unit 33 estimates the first channel information by substituting the training signal C for X_1 in Equation 1. The channel estimation unit 33 stores a training signal and P_s1 in advance. The channel estimation unit 33 calculates an estimated value {H_11} of the first channel information using an estimation method such as the LS method or the LMMSE method based on the stored value and the received training signal. In slot 1, relay station 1-2 does not transmit a training signal. Therefore, the channel estimation part 33 can estimate 1st channel information based on the training signal which has not received interference. Therefore, the channel estimation unit 33 can estimate the first channel information with high accuracy.

  Next, the channel estimation unit 33 estimates second channel information. The channel estimation unit 33 performs processing on the premise that the channel response (H_sd) between the transmission station 1-1 and the destination station 1-3 is constant during the period of slot 1 and slot 2. Since the period of slot 1 and slot 2 is short, the change in channel response is very small. Therefore, even if processing is performed based on such assumptions, there is no significant adverse effect on the estimation accuracy of channel information. When Expression 5 and Expression 7 are modified based on such a premise, Expression 8 shown below is obtained. The channel estimation unit 33 calculates the estimated value {H_22} of the second channel information by substituting the calculated {H_11} and the previously stored P_s1 and P_s2 with respect to Equation 8 below.

  That is, the channel estimation unit 33 sets the ratio of the transmission power P_s1 of the signal P1 in the slot 1 and the transmission power P_s2 of the signal P2 in the slot 2 (the ratio of the square root of each value) to the estimated value {H_11 of the first channel information }, The estimated value {H_22} of the second channel information is calculated.

  Next, the channel estimation unit 33 estimates third channel information. Hereinafter, two estimation processes (a first estimation process and a second estimation process) will be described for the third channel information estimation process. The channel estimation unit 33 may estimate the third channel information by performing the first estimation process, or may estimate the third channel information by performing the second estimation process.

<First estimation process>
By subtracting {H — 22} C on the right and left sides of Equation 3, Equation 9 is obtained. C is a training signal stored in advance by the channel estimation unit 33.

  The second term on the right side of Equation 9 is a noise component due to the estimation error, and the third term on the right side of Equation 9 is the noise component AWGN. In the first estimation process, the channel estimation unit 33 performs estimation assuming that the values of these two terms are zero. Since the value of any term is zero in the ideal state, the estimation accuracy is not greatly adversely affected even if the estimation process is performed under such a premise.

  The channel estimation unit 33 that performs the first estimation process estimates the value of the third channel information H_21 by substituting the training signal received in slot 2 for Y_d2 of Equation 9. That is, the channel estimation unit 33 that performs the first estimation process subtracts the multiplication result of the training signal and the estimated value of the second channel information from the combined signal received in slot 2. Then, the channel estimation unit 33 estimates the third channel information based on the ratio between the subtraction result and the training signal stored in advance.

<Second estimation process>
In Equation 4, when Y_d1 (the training signal received in slot 1) is multiplied by a predetermined coefficient (transmission power ratio: [P_s2] / [P_s1]) and subtracted from Y_d2 (the training signal received in slot 2) Equation 10 is obtained.

  Here, both the transmission power (P_s1) of the transmission station 1-1 in the slot 1 and the transmission power (P_s2) of the transmission station 1-1 in the slot 2 are previously determined by the channel estimation unit 33 of the destination station 1-3. It is remembered. The value of the second term on the right side and the value of the third term on the right side are both noise components AWGN. In the second estimation process, estimation is performed by regarding the values of these two terms as zero. Since the value of any term is zero in the ideal state, even if such estimation processing is performed, there is no significant adverse effect on the estimation accuracy.

  The channel estimation unit 33 that performs the second estimation process estimates the third channel information based on Equation 10. That is, the channel estimation unit 33 that performs the second estimation process subtracts the multiplication result of the training signal received in slot 1 and the transmission power ratio from the training signal in the combined signal received in slot 2. Then, the channel estimation unit 33 estimates the third channel information based on the ratio between the subtraction result and the training signal stored in advance.

  FIG. 6 is a flowchart showing a processing flow of the destination station 1-3 of the cooperative transmission system 1 according to the embodiment of the present invention. First, the baseband conversion unit 32 receives the signal P1 via the antenna 31 at the timing of slot 1 (step S101). Next, the baseband conversion unit 32 receives the combined signal via the antenna 31 at the timing of slot 2 (step S102). The baseband conversion unit 32 converts each received signal from the passband to the baseband.

  The channel estimation unit 33 estimates the first channel information based on the training portion of the signal P1 received in the slot 1 (step S103). Next, the channel estimation part 33 estimates 2nd channel information based on the estimated value of 1st channel information (step S104). And the channel estimation part 33 estimates 3rd channel information based on the training part of the synthetic | combination signal received by slot 2 (step S105).

  The data demodulator 34 equalizes the channel of the signal based on the result of channel estimation by the channel estimator 33, and performs data demodulation processing (step S106). The data demodulator 34 generates a detection value corresponding to each complex QAM symbol by performing data demodulation processing. The channel decoding unit 35 performs channel decoding processing based on the detection value (step S107). By executing the channel decoding process, the channel decoding unit 35 restores the information bit stream that is the transmission target in the transmission station 1-1.

Hereinafter, effects of the destination station 1-3 configured as described above will be described.
In the slot 2, the signal transmitted from the transmission station 1-1 and the signal transmitted from the relay station 1-2 are combined and received by the destination station 1-3. Therefore, mutual interference also occurs in the training signal portion of each signal. Therefore, in the conventional cooperative transmission system, H_21 and H_22 cannot be properly estimated in the destination station 1-3. On the other hand, the destination station 1-3 of the cooperative transmission system 1 according to the embodiment of the present invention can accurately estimate not only H_11 but also the values of H_21 and H_22 with the above-described configuration. That is, the destination station 1-3 having the above configuration can separate the training signals received from the transmission station 1-1 and the relay station 1-2, and improve the estimation accuracy of the channel information.

<Modification>
There are various types of multi-carrier systems. For example, there are OFDM (Orthogonal Frequency Division Multiplexing) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Multi-Carrier Code Division Multiple Access (MC-CDMA) systems, and the like. . The processing of the channel estimation unit 33 described above may be applied to these multicarrier schemes.

  In the cooperative transmission system 1 described above, the AF method is applied as the relay station forward method. However, other relay station forward methods may be applied. For example, a CF (Compress-and-Forward) method, a DF method, or the like may be applied.

In the cooperative transmission system 1 described above, each radio station has one antenna. That is, an application example of a SISO (Single Input Single Output) system has been described. On the other hand, all or some of the wireless stations may be configured to have a plurality of antennas. That is, the cooperative transmission system 1 may be configured as a MIMO system.
The configuration of the cooperative transmission system 1 described above is 1R2H, but the configuration of the cooperative transmission system 1 is not limited to this.
In the configuration of the cooperative transmission system 1 described above, the channel estimation unit 33 stores known values (P_s1, P_s2, and P_r2) in advance, but the channel estimation unit 33 performs the above-described processing based on information included in the received signal. A known value may be acquired.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Cooperative transmission system, 1-1 ... Originating station, 1-2 ... Relay station, 1-3 ... Destination station, 11 ... Channel encoding part, 12 ... Data modulation part, 13 ... Distribution part, 14 ... Training addition part , 15 ... Passband converter, 16, 31 ... Antenna, 32 ... Baseband converter, 33 ... Channel estimator, 34 ... Data demodulator, 35 ... Channel decoder

Claims (4)

A first signal transmitted from the transmitting station at a first timing, a second signal transmitted from the transmitting station at a second timing that arrives after the first timing, and a relay station at the second timing A signal receiving unit for receiving the first signal relayed by
Channel information relating to the first signal transmitted from the transmitting station at the first timing based on a known signal included in the first signal transmitted from the transmitting station at the first timing. A first channel estimator for estimating channel information;
The estimation result of the first channel information, the first transmission power that is the transmission power when the transmission station transmits the first signal at the first timing, and the transmission station at the second timing Based on the second transmission power that is the transmission power at the time of transmitting the second signal, second channel information that is channel information related to the second signal transmitted from the source station at the second timing is estimated. A second channel estimation unit;
The known signal included in the first signal transmitted from the transmission station at the first timing and relayed by the relay station at the second timing and the first signal transmitted from the transmission station at the second timing. Two signals transmitted from the source station at the first timing based on a combined signal of known signals included in two signals , an estimation result of the second channel information, and a previously stored known signal . A third channel estimation unit that estimates third channel information that is channel information related to the first signal relayed by the relay station at the timing of:
Destination station comprising. A first signal transmitted from the transmitting station at a first timing, a second signal transmitted from the transmitting station at a second timing that arrives after the first timing, and a relay station at the second timing Receiving the first signal relayed by: a signal receiving step;
Channel information relating to the first signal transmitted from the transmitting station at the first timing based on a known signal included in the first signal transmitted from the transmitting station at the first timing. A first channel estimation step for estimating channel information;
The estimation result of the first channel information, the first transmission power that is the transmission power when the transmission station transmits the first signal at the first timing, and the transmission station at the second timing Based on the second transmission power that is the transmission power at the time of transmitting the second signal, second channel information that is channel information related to the second signal transmitted from the source station at the second timing is estimated. A second channel estimation step;
The known signal included in the first signal transmitted from the transmission station at the first timing and relayed by the relay station at the second timing and the first signal transmitted from the transmission station at the second timing. Two signals transmitted from the source station at the first timing based on a combined signal of known signals included in two signals , an estimation result of the second channel information, and a previously stored known signal . A third channel estimation step of estimating third channel information which is channel information related to the first signal relayed by the relay station at the timing of
A channel estimation method comprising: A first signal transmitted from the transmitting station at a first timing, a second signal transmitted from the transmitting station at a second timing that arrives after the first timing, and a relay station at the second timing A signal receiving unit for receiving the first signal relayed by
Channel information relating to the first signal transmitted from the transmitting station at the first timing based on a known signal included in the first signal transmitted from the transmitting station at the first timing. A first channel estimator for estimating channel information;
The estimation result of the first channel information, the first transmission power that is the transmission power when the transmission station transmits the first signal at the first timing, and the transmission station at the second timing Based on the second transmission power that is the transmission power at the time of transmitting the second signal, second channel information that is channel information related to the second signal transmitted from the source station at the second timing is estimated. A second channel estimation unit;
Said known signal included in the first signal transmitted from the originating station by the first timing, which is relayed by the relay station transmitted the second timing from the originating station by the first timing and the combined signal with a known signal included in the second signal transmitted from the originating station by the known signal and the second timing included in said first signal, the first transmission power and the second transmission power and A third channel which is channel information related to the first signal transmitted from the transmission station at the first timing and relayed by the relay station at the second timing based on a known signal stored in advance A third channel estimator for estimating information;
Destination station comprising. A first signal transmitted from the transmitting station at a first timing, a second signal transmitted from the transmitting station at a second timing that arrives after the first timing, and a relay station at the second timing Receiving the first signal relayed by: a signal receiving step;
Channel information relating to the first signal transmitted from the transmitting station at the first timing based on a known signal included in the first signal transmitted from the transmitting station at the first timing. A first channel estimation step for estimating channel information;
The estimation result of the first channel information, the first transmission power that is the transmission power when the transmission station transmits the first signal at the first timing, and the transmission station at the second timing Based on the second transmission power that is the transmission power at the time of transmitting the second signal, second channel information that is channel information related to the second signal transmitted from the source station at the second timing is estimated. A second channel estimation step;
Said known signal included in the first signal transmitted from the originating station by the first timing, which is relayed by the relay station transmitted the second timing from the originating station by the first timing and the combined signal with a known signal included in the second signal transmitted from the originating station by the known signal and the second timing included in said first signal, the first transmission power and the second transmission power and A third channel which is channel information related to the first signal transmitted from the transmission station at the first timing and relayed by the relay station at the second timing based on a known signal stored in advance A third channel estimation step for estimating information;
A channel estimation method comprising:

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